Communication receivers that recover digital signals must sample an analog waveform and then reliably detect the sampled data. Signals arriving at a receiver are typically corrupted by intersymbol interference (ISI), crosstalk, echo, and other noise. As data rates increase, the receiver must both equalize the channel, to compensate for such corruptions, and detect the encoded signals at increasingly higher clock rates. Decision-feedback equalization (DFE) is a widely used technique for removing intersymbol interference and other noise at high data rates.
Generally, decision-feedback equalization utilizes a nonlinear equalizer to equalize the channel using a feedback loop based on previously detected (or decided) data. In one typical DFE-based receiver implementation, a received analog signal is sampled after DFE correction and compared to one or more thresholds to generate the detected data.
To improve the performance of DFE-based receiver, the receiver includes an analog front end (AFE) having a variable gain amplifier (VGA), used to control the input signal level, and an equalizer used to compensate for linear, frequency-based distortions in the input signal to the receiver. The equalizer (also referred to herein as a continuous time linear equalizer or CTLE) is generally implemented as an analog-based filter with at least one adjustable coefficient or peaking parameter that can at least partially compensate for linear distortions in the received signal. However, the analog circuitry in the AFE might have inherent limitations, one of which is the amount of nonlinear distortion introduced onto the received signal by various analog circuits in the AFE. Any distortion introduced by the AFE can seriously degrade performance of the overall receiver.